1. Field of the Invention
The instant disclosure is related to a light-emitting diode circuit, and more particularly to a light-emitting diode circuit capable of operating with at least two different voltage sources and a light-emitting device having the same.
2. Description of Related Art
Traditional emergency lamps having direct current (DC)-based light-emitting diodes (LEDs) incorporated are generally driven by driving circuits for the DC-based light-emitting diodes. Under normal circumstances when the supply of an alternating current (AC) power is not interrupted, a secondary battery of the emergency lamp is charged so that the secondary battery may be used to properly power the DC-based light-emitting diodes when the supply of the AC power is interrupted in the event of an external power outage. Please refer to FIG. 1, which illustrates a circuit block diagram of a traditional DC-based light-emitting device 1 having the DC-based light-emitting diodes. The light-emitting device 1 includes a rectifier 11, a load unit 12, a battery charging circuit 13, an alternating current (AC) voltage detecting circuit 14, and a voltage booster circuit 15. The load unit 12 may include a plurality of the light-emitting diodes. The rectifier 11 is configured to receive an AC voltage and electrically coupled to the load unit 12 and the AC voltage detecting circuit 14. The load unit 12 is further electrically coupled to the battery charging circuit 13 and the voltage booster circuit 15. The booster circuit 15 is electrically coupled to the battery charging circuit 13 and the AC voltage detecting circuit 14.
When the light-emitting device 1 is operated under an external AC power source, if the DC-based LEDs of the load unit 12 are of low voltage driven type (9-24 Volts), the rectifier 11 would be configured to rectify the external AC power to a low voltage ranging from 9 volts to 24 volts, so that the DC-based light-emitting diodes of the load unit 12 may be driven at lower voltage. If the DC-based light-emitting diodes of the load unit 12 are of high voltage driven type (such as a voltage that is larger than 24 volts), the rectifier 11 would need to cooperate with the AC voltage detecting circuit 14 and the voltage booster circuit 15 to drive the DC-based light-emitting diodes of the load unit 12. The secondary battery of the battery charging circuit 13 may be charged while the light-emitting diodes of the load unit 12 are turned on.
On the other hand, when external AC power is not available, if the DC-based light-emitting diodes of the load unit 12 are of low voltage driven type (at a voltage between 3.7 volts to 24 volts), the secondary battery of the battery charging circuit 13 may directly power the DC-based LEDs of the load unit 12 at a lower voltage (3.7-24 volts). If the DC-based light-emitting diodes of the load unit 12 are of high voltage driven type (larger than 24 volts), the power provided by the secondary battery of the battery charging circuit 13 would have to be further boosted up by the voltage booster circuit 15 before the boosted-up power is delivered to drive the light-emitting diodes of the load unit 12. Moreover, the DC-based light-emitting device 1 could be used as a portable light source. When the mobile lighting device is not in connection with the AC power, the secondary battery embedded therein could provide power for driving the light-emitting device 1.
The dual-mode power supply can be implemented by a combination of the rectifier 11 and the voltage booster circuit 15. However, the presence of the rectifier 11 and the voltage booster circuit 15 could complicate the circuitry design of the light-emitting device 1 and also increase the manufacturing cost thereof.